Add contrast pill to workspace apps

When the flag is enabled, allow the BubbleTextView to draw a background
pill behind the app title. Also change the color of the text to properly
ensure contrast.  The contrast pill is only enabled for workpace apps,
so attempt draw the pill only for DoubleShadowBubbleTextView elements.

Bug: 341217082
Flag: com.android.launcher3.enable_contrast_tiles
Test: Manual, visual change
Change-Id: Idce27bd8dfca4b525c762fcd0873562f31b45b8f